title: The natural course of spontaneous osteonecrosis of the knee (SPONK): a 1- to 27-year follow-up of 40 patients.
abstract: OBJECTIVE
  Spontaneous osteonecrosis of the knee (SPONK) is a painful lesion in the elderly, frequently leading to osteoarthritis and subsequent knee surgery. We evaluated the natural course and long-term consequences of SPONK in terms of need for major knee surgery.
  
  
  METHODS
  Between 1982 and 1988, 40 consecutive patients were diagnosed with SPONK. The short-term outcome has been reported previously (1991). After 1-7 years, 10 patients had a good radiographic outcome and 30 were considered failures, developing osteoarthritis. In 2012, all 40 of the patients were matched with the Swedish Knee Arthroplasty Register (SKAR) and their medical records were reviewed to evaluate the long-term need for major knee surgery.
  
  
  RESULTS
  At the 2012 review, 33 of the 40 patients had died. The mean follow-up time from diagnosis to surgery, death, or end of study was 9 (1-27) years. 17 of 40 patients had had major knee surgery with either arthroplasty (15) or osteotomy (2). All operated patients but 1 were in the radiographic failure group and had developed osteoarthritis in the study from 1991. 6 of 7 patients with large lesions (> 40% of the AP radiographic view of the condyle) at the time of the diagnosis were operated. None of the 10 patients with a lesion of less than 20% were ever operated.
  
  
  CONCLUSIONS
  It appears that the size of the osteonecrotic lesion can be used to predict the outcome. Patients showing early signs of osteoarthritis or with a large osteonecrosis have a high risk of later major knee surgery.
authors.affiliation: Department of Orthopedics, Clinical Sciences, Lund University and Skåne University Hospital, Lund, Sweden. jan.jureus@med.lu.se
authors.forename: Jan
authors.initials: J
authors.lastname: Juréus
authors.forename: Anders
authors.initials: A
authors.lastname: Lindstrand
authors.forename: Mats
authors.initials: M
authors.lastname: Geijer
authors.forename: Otto
authors.initials: O
authors.lastname: Robertsson
authors.forename: Magnus
authors.initials: M
authors.lastname: Tägil
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000453:epidemiology / Q000209:etiology*; D010020:Osteonecrosis / Q000000981:diagnostic imaging* / Q000601:surgery; D011379:Prognosis; D011859:Radiography; D016019:Survival Analysis